1. Field of the Invention
The present invention relates to a silicon crystal, and a device and method for manufacturing the same.
2. Description of the Related Art
Silicon crystals include single crystalline silicon and polycrystalline silicon.
The single crystalline silicon is used as a starting material for manufacturing a semiconductor device such as LSI. In recent years, it has been strongly desired to manufacture a high purity single crystalline silicon with large diameter at a low cost.
The single crystalline silicon is generally manufactured by use of a CZ type crystal growing device or FZ type crystal growing device. The CZ type crystal growing device is a device most frequently used for the manufacture of single crystalline silicon. This device generally has a structure in which starting polycrystalline silicon is put into a quartz glass crucible followed by melting, and the resulting single crystalline silicon is lifted up from the melt surface. As the heating means, a carbon heating element is used, and the silicon is melted by indirect heating from the circumference of the crucible. A carbon-made holder is arranged on the outside of the quartz glass crucible in order to keep the shape.
According to this method, the quartz crucible is heated to a temperature equal to or higher than the melting point (1413.degree. C.) of silicon. Therefore, silicon dioxide of which the quartz glass crucible is composed is eluted into the silicon melt, resulting in the incorporation of oxygen into the single crystalline silicon to be lifted up. The oxygen contained in the single crystalline silicon often effectively acts in the manufacturing process of a device to achieve intrinsic gettering function or the like, but disadvantageously increases crystal defects in a silicon wafer when a large quantity is contained.
On the other hand, the general FZ type crystal growing device adapts a method of passing a polycrystalline silicon preliminarily formed in bar into a high frequency coil having an inside diameter of several centimeters from above, and locally heating and melting it to grow the single crystalline silicon downward.
According to this method, since the melt part does not directly make contact with the quartz glass member, the oxygen incorporated into the crystal can be extremely minimized.
As described above, the oxygen concentration in the single crystalline silicon could not be sufficiently reduced in the CZ type crystal growing device. In the manufacture of a crystal with large diameter, particularly, the heating temperature had to be raised since the quartz crucible is enlarged. Therefore, the deformation of the crucible and the elution of silicon dioxide from the crucible wall were increased, and a large quantity of oxygen was incorporated into the crystal, which had a significant influence on the quality of the single crystalline silicon.
Various countermeasures have been thus made such as thickening of the quartz glass crucible to prevent the deformation of the crucible, application of a magnetic field to the silicon melt to control the melt convection, reduction of the friction between the crucible wall and the silicon melt to prevent the elution of silicon dioxide from the crucible wall, and the like. However, these leaded to a significant increase in manufacturing cost, and could not provide a sufficient effect for it.
In contrast to this, the FZ type crystal growing device can control the oxygen concentration to a low level. However, the diameter of the to be single crystalline silicon grown was limited in the FZ type crystal growing device, and a single crystalline silicon with large diameter could not be manufactured.